Pacific Coast Iris Culture
Choosing a Site:
In the garden, PCI develop most easily under conditions similar to those of their natural habitat — that is, in lightly wooded areas and on sloping ground that is gritty, well drained, neutral to slightly acidic, and has considerable humus. Moisture comes mainly during the winter months and summers are normally long and dry, with most moisture from summer rain or thundershowers or as drip from dew. When possible it’s best to try to mimic these conditions.
The most important factor in the garden is good drainage. PCIs are not wetland plants and will not tolerate soggy growing conditions. The combination of moisture and heat promotes root damage and various diseases from which these plants cannot recover. Frequent summer watering is not needed, especially if mulch is applied. PCIs can grow naturally in a wide range of soils, but tend to do best in slightly to moderately acid (pH 5.5 to 6.5) soil.
The amount of sun Pacifica Iris will tolerate largely depends on the location. PCI in gardens located near the coast, and towards the northern part of their range, can tolerate full sun. But in most climates, plant them in part shade, where they can receive morning sun but are shaded during the hottest part of the day. For warmer climates like Southern California, full shade is advised. They thrive under dry shade conditions during summer and are great understory plants for oaks and sycamores. Remember to avoid the often deadly combination of heavy moisture and heat.
If your soil is not naturally acidic and well drained, consider a raised bed with amended soil, using organic matter or coarse sand to open up finer soils. Mixing in a well drained garden soil mix with native soil in raised beds also works.
Planting and Care:
PCIs are most successfully planted and transplanted when their roots are plump, white, and actively growing. This happens when they receive rain and supplemental irrigations if it’s a dry year. Late fall and early spring are the best seasons to transplant based on natural rainfall on the west coast. To tell if your PCIs are ready for lifting, scratch away some soil from around the base of the plants and search for new white roots. It is best to transplant a multi-rhizome division, as single rhizomes often fail.
Dig a good size hole. Depending on your soil type, it can be advantageous to mix some compost, organic matter or amendments that improve drainage into the hole. When planting, take care not to break the white roots and keep the root balls intact. In most gardens, plant your PCI with the rhizomes/shoots crown at the soil line. In heavier soil conditions like clay, plants should be raised slightly above the soil line in a slight mound to improve drainage. If you have rodents, lining the hole with chicken wire can help the plants establish themselves. Water in new plants well and keep them slightly moist for the first week.
In most areas, regular summer watering after planting is required to keep plants alive, but take care not to water midday in hot weather: this promotes fungi that kill PCI. During the first summer in your garden, water new PCI plants every week to two weeks, unless it rains regularly. Water PCI in early morning, or late afternoon to evening in hot weather, with cool to cold water. Water pH should be neutral or acidic. Avoid watering with water that has been softened with salts for household use; PCI, and many other garden plants, do not like softened water.
Mulches around your plants are also advised, especially under severe (hot or cold) temperatures. Mulch helps regulate the soil temperature, keeping the roots cool in the summer and warm in the winter. It also helps conserve soil moisture and provides additional carbon for soil microbes. Once established in your garden, mulch also helps PCIs withstand considerable freezing.
If desired, fertilizer can also be used in winter or early spring during the plant’s growing season. Top dress each spring with compost and mulch and/or use 10-10-10 time release fertilizer.
Bloom season varies according to latitude. Flowering in warm Southern California gardens usually starts in late winter through the end of spring with a peak in April. In the cooler regions of the Pacific Northwest, PCI begin blooming later, and flower into May and June.
Dividing and Sharing Plants:
Check the roots by gently pushing aside the soil to look at the growing front of the green fans of leaves. If you see abundant new white roots, it’s time to dig. Roots grow mid fall to early winter and late winter to early spring, depending on the local climate and moisture levels.
When dividing, gardeners suggest leaving one half of the parent plant undisturbed in case transplants don’t survive. The remaining portion of the parent plant will continue to grow.
PCI plants grow in clusters of fans, with thin small rhizomes connecting each cluster to the rest. After lifting the plant, carefully remove soil around clusters, keeping new roots intact. Chop or cut through the connecting older rhizomes, and lift the clusters to transplant with as many fresh roots, and some old roots, as possible. Trim the old rhizomes back, and cut off old, dead fans. Cut off old leaves, and if shipping to another garden, cut the healthy green leaves back to four or five inches long. It is vital to keep the roots moist until they are back in the ground. Unlike bearded irises with thick rhizomes, PCI cannot be out of the ground for weeks.
The divisions can be immediately replanted in preferred soil conditions outlined in the section above. They can also be placed into small pots consisting of 75% perlite/ 25% peat to allow time to root out before transplanting to larger containers or placing them into the ground. Some commercial growers soak roots in solutions of B-1 before planting, which improves survival and encourages growth.
If rhizomes are being shipped, send divisions out promptly to arrive by the fastest available shipping method. Commercial growers have found success shipping these rhizomes in moisture-releasing soil mixture, peat, or even damp paper towels in bags. Others have shipped divisions in small plastic pots filled with well-drained media such as perlite. They should be planted immediately upon receipt.
Growing PCI in Containers
Container growing is successful if the conditions PCI like can be created: moderately acidic, good drainage, cool soil temperatures. For areas with very cold winters this offers the advantage that the containers can be brought into a cool greenhouse for the winter. Likewise for climates that run hot, PCIs have been successfully brought into bright shade indoors during the flowering season to keep the plants cool.
Matilija Nursery is very successful with container grown PCI. The nursery uses five gallon nursery pots; keeps pots in midday shade; and adds perlite to the soil mix. The nursery waters its containers fall through spring, every week until flowering stops, then waters every other week through the summer. They fertilize regularly, because these plants do not have access to the nutrients that would be present in the potting soil.
All PCI grow well in pots for one to two years from seed; around year three, they may begin to die. This may be due to several factors: breakdown of potting soil leading to poor aeration and water logging, and hot soil, which leads to over-heated roots. Coarse mixtures are important for good drainage in containers. Use fine gravel, coarse sand or perlite to improve drainage of the soil mix. We recommend a 1:1 ratio of soil mix to coarse additive.
Generally, large pots or planters (five gallon or larger) work well if pots are in shade for the warm part of the day, and not too cold in winter. This should be enough room for one plant for four to five years. Plan on repotting when plants reach the edge of their container. Mulch the surface to help the roots stay cool.
Water weekly until flowering ends, then water every other week throughout the summer.
Learn more about starting PCIs from seed!
Read more about hybridizing and judging Pacifica Hybrids.